Parasite localization and dissemination in the Babesia-infected host.

Babesia bovis infections in cattle and B. canis infections in dogs are characterized by non-haemolytic anaemia and low parasitaemia during the acute phase of the disease. In this phase of the disease, animals suffer from hypotension followed by disturbances of the coagulation system. This review discusses the hypothesis that may explain the process of parasite localization in the host, and the consequences of such localization. It is suggested that hypotension favours the interaction between infected erythrocytes and the endothelial lining, thus facilitating localization of the infection. In addition, activation of the coagulation system by a parasite-derived molecule (one associated with the surface of infected erythrocytes or a soluble antigen) might consolidate this situation by causing cellular plugs to form. The continued proliferation of parasites in such plugs may then result in the occurrence of capillaries that are particularly heavily parasitised. An explanation is also suggested for the protective effect of vaccines against clinical babesiosis, based on the soluble parasite antigens that are released into the medium in cultures of babesial parasites.